The invention relates to a fuel injection device, especially for diesel internal combustion engines with direct injection.
Such fuel injection devices are disclosed, for example, in my U.S. Pat. No. 4,222,358. The stepped piston utilized in this fuel injection device provides the high fuel pressure necessary for the injection while the injection distributor pump connected ahead takes over the fuel distribution at a medium level pump pressure. The fuel pump required for such a fuel injection system accordingly needs to produce only a medium pressure and furthermore can operate with greater delivery quantities, whereby a substantially greater precision in the fuel regulation is made possible with the use of conventional distributor injection pumps.
In this known fuel injection device, a working chamber in the form of a bore associated with the smaller end face of the stepped piston is filled on the side of the injection valve by way of a connecting bore passing through the stepped piston, a ball valve fashioned as a check valve being arranged in this bore. However, since only a portion of the quantity of fuel supplied by the injection distributor pump, corresponding to the area ratio between the surface areas at the end faces of the stepped piston, is passed on from the stepped piston via the ball valve to the injection valve, measures must be taken to remove the residual portion of the metered quantity of fuel. In the known device, this proportion of the fuel would have to be returned into the fuel feed duct emanating from the injection distributor pump during the reverse, or return, movement of the stepped piston, and would have to be discharged from this duct by appropriate means. This, though, can lead to considerable difficulties. Moreover, the arrangement of a ball valve in the stepped piston will most probably be very difficult from an engineering standpoint.